P15610: Digital Microfluidics Control System
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Detailed Design

Table of Contents

Housing

Overview

Due to weight concerns with the first sample enclosure received, the team continued to investigate possible enclosures and arranged to receive a sample from a new vendor. The following is a comparison of the two enclosures.

Comparison of Enclosure Samples

Comparison of Enclosure Samples

Aluminum Enclosure

Aluminum Enclosure

Steel Enclosure

Steel Enclosure

The critical component of the grounding system will be a 104-PR-5A Miniature Circuit Breaker. This will provide a central overcurrent protection for all system components. Each section of the housing will be wired to this breaker, and the system will not operate if any ground connection is broken. The datasheet for this part can be found here

Drawings and Schematics

The purchased enclosures will require modification in order to accept ports and hardware during assembly. The necessary drawings for machining can be found by clicking the links below.

Lower Tier (Power)

Middle Tier (Amplifier)

Upper Tier (Input/Output)

Front View

Front View

Rear View

Rear View

Exploded View

Exploded View

Bill of Material (BOM)

The Bill of Materials for the housing is shown below. The expected cost of the housing is less than the budgeted cost by about $43. The expected cost does not include discounts that would be received from purchasing from Allied Electronics.
Bill of Material for Housing

Bill of Material for Housing

Test Plans

Parts necessary

I/O Boards and Control Board

Prototyping, Engineering Analysis, Simulation

The design of the Control Board (with attached Frequency Generator) and Output Board are identical to the High-Voltage Switching Board of the DropBot project, available here, here and here.

The design of the Input Board has been changed from the previous stage; the Input Board now measures capacitance by an attachment to the ground plane of the DMF chip and as such no longer requires 40 FETs for control purposes. These 40 FETs have been replaced by one solid-state relay which connects the ground plane to either ground while not reading, or the input board circuit for measuring capacitance and resistance. Both the magnitude and phase of the complex impedance are turned into steady-state DC voltages for the Arduino to read.

SPICE models of the components used in the Input Board were found, and the circuit simulated in OrCAD PSPICE for functionality. Simulated output voltages of the measurement of 5KOhm/200pF, 15KOhm/50pF, 15KOhm/51pF, 15.1Kohm/50pF, and 25KOhm/1pF resistor/capacitor combinations are presented below. In addition, phase measurements for a 15KOhm/50pF and 15Kohm/55pF load are shown.

Output Voltage over time for 5KOhm/200pF load

Output Voltage over time for 5KOhm/200pF load

Output Voltage over time for 25Kohm/1pF load

Output Voltage over time for 25Kohm/1pF load

Output Voltage over time for 15KOhm/51pF load

Output Voltage over time for 15KOhm/51pF load

Output Voltage over time for 15.1Kohm/50pF load

Output Voltage over time for 15.1Kohm/50pF load

Output Voltage over time for 15KOhm/50pF load

Output Voltage over time for 15KOhm/50pF load

Phase measurement of 15Kohm/55pF load

Phase measurement of 15Kohm/55pF load

Phase measurement of 15Kohm/50pF load

Phase measurement of 15Kohm/50pF load

Drawings and Schematics

Schematic of output board as provided by DropBot

Schematic of output board as provided by DropBot

Schematic of control board as provided by DropBot

Schematic of control board as provided by DropBot

Schematic of input circuit without solid-state relay, measuring capacitance Cmeasure and resistance Rmeasure

Schematic of input circuit without solid-state relay, measuring capacitance Cmeasure and resistance Rmeasure

Bill of Material (BOM)

The Output Board is likely to be the most expensive part of the project, given that the 40 solid-state relays it must have for operation are several dollars each. These solid-state relays have been chosen for proven use (they are identical to the DropBot SSRs) and switching speed of 0.28ms.

BOM of Control Board

BOM of Control Board

BOM of Input Board

BOM of Input Board

BOM of Output Board

BOM of Output Board

Test Plans

Control Board

First, the Arduino will be instructed to output high voltage on certain pins, and an oscilloscope will measure those outputs as between 3.3V and 6V. Next, the Arduino will be instructed to control the frequency generator to provide a 9V amplitude, 50KHz signal, and the oscilloscope will be used to assure those signals come from the frequency generator. Lastly, the Arduino's ADC will be fed stable 0V, 1V, 2V, 3V, 4V, and 5V DC inputs, and then the resulting value will be read from memory and assured to be within 5 bits of 0x000, 0x0CD, 0x19A, 0x266, 0x333, and 0x400 (respectively) to assure the requirement of 1pF capacitance granularity.

Parts Required:

Input Board

Construct input board circuit on breadboard as closely as possible, replacing surface-mount parts with equivalent axial parts.

Measure a known capacitance on the order of 47pF alongside a known resistance on the order of 15KOhms.

Measure known capacitances on the range from 1pF to 200pF alongside a known resistance on the order of 15KOhms.

Measure known resistances on the range from 5KOhms to 25KOhms alongside a known capacitance on the order of 47pF.

Measure highest and lowest output values using different capacitances and resistances as available.

Construct the input board circuit on the purchased PCB, with all parts as in the BOM.

Parts Required:

Output Board

The output board's shift registers will have a very slow (~0.5Hz) clock signal attached to their clock inputs, and one or two bits of the signal input will be high (these will be done with a DC power supply and signal generator). The "high voltage" input (which in the full project will be 120Vrms) will be attached to a steady 5VDC. The outputs will be "chased" by a string of four to six LEDs, to visually indicate that the high voltage signal can flow through the output board to the correct output pins.

If the previous test is successful, the high voltage input will be changed to 5V peak-to-peak AC, and the clock signal disconnected. A voltage divider will be placed on a pin output which receives the high voltage input, and the divided voltage measured by an oscilloscope. The input high voltage AC will be increased, assuring circuit functionality, until reaching 120Vrms. The AC voltage will be provided by a signal generator and a transformer.

If the previous set of tests is successful, a two-input oscilloscope will be attached to the output of one pin output, and the input clock signal to the shift registers. The time between the rising clock and the appearance of sinusoidal DC signal at the output will be quantified and checked to be between 0.25ms and 0.5ms.

Opto-Isolator circuit for HV Output

Opto-Isolator circuit for HV Output

Parts Required:

Amplifier and Power Supply

Prototyping, Engineering Analysis, Simulation

The Signal Generator board design will be identical to the previous DropBot's project. Which can be found here.

The Signal Generator has been re-purposed for this project: it will provide the low voltage high frequency signal for the amplifier that will be sent out to the DMF device, and provide a low voltage varying frequency to the DMF device to measure the capacitance on an electrode via Input Board.

300 Hz - 100kHz Frequency Response of Step Up Transformer (1:14 192uH)

300 Hz - 100kHz Frequency Response of Step Up Transformer (1:14 192uH)

Drawings, Schematics, Flow Charts, Simulations

Schematic of signal generator board as provided by DropBot

Schematic of signal generator board as provided by DropBot

Schematic of Step Up Transformer for High Voltage output

Schematic of Step Up Transformer for High Voltage output

Schematic of

Schematic of "Push-pull" amplifier

Bill of Material (BOM)

The power amplifier will be the most expensive in this part because of the increased cost of high voltage components and PCB to be created. The power supplies are costly because they are capable supplying 2A of current, which will be needed to handle the possible demand of multiple output boards in the future.
BOM of Signal Generator Board

BOM of Signal Generator Board

BOM of Power Supplies

BOM of Power Supplies

Cosel +5 V Power Supply

Cosel +5 V Power Supply

Cosel +/-15 V Power Supply

Cosel +/-15 V Power Supply

BOM of Amplifier

BOM of Amplifier

Test Plans

Amplifier

Test current limiting circuit

Test linear regulator circuit, the circuit is only active when FAULT input is LOW.

Test the High Voltage Amplifier circuit with input connected to signal generator.

Combine current limiting circuit and regulator circuit, test the output voltage of the combined circuit.

Combine all sub-circuits above to create an amplifier system.

Combine signal generator, amplifier system, and transformer. Vary the frequency (100 Hz ~ 100 kHz) of the signal generator and test the circuit for alternating output voltages, record data. Calculate amplifier frequency response up to 100 kHz.

Power Supply

A digital multi-meter will be used to manually check the DC voltages at each output of the +12V, -12V and +5 V terminals. When the power supplies are turned on, there will be an LED indicating which output rails are connected. There are short-circuit safety measures embedded in the power supplies that will prevent damage on our devices. +- 15 V with a tolerance of 1% is acceptable +5 V with a tolerance of 1% is acceptable Over current protection limits the current to 5 Amps

Equipment

Risk Assessment

After proceeding through this stage, the risk assessments identified in the Subsystem Level Phase did not change. A link to the Risk Assessments established for this project can be found here: Risk Assessment.

Detailed Design Project Plan

The following is the team project plan for the next phase. This will be the basis of the team's activities for the next 3 weeks.
Project Plan for Phase 4

Project Plan for Phase 4

Complete Bill of Materials

The combined Bill of Materials for each subsystem can be found here: Complete Bill of Materials.

MSDII Project Plan

The following is the team project plan for MSDII. This will be the basis of the team's activities for the MSDII course.
MSDII Project Plan

MSDII Project Plan


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